1. Field of the Invention
This invention is directed to a device and method for sampling an analog input signal(s) to generate a sample, and for providing the sample to a memory in a direct memory access (DMA) operation.
2. Description of the Related Art
DMA sampling systems generally function to sample an analog input signal from a sensor to generate samples which are provided to a memory in a DMA operation. Such systems periodically request bus mastership from a central processing unit (CPU) which is coupled to a memory by a bus. Upon a grant of bus mastership by the CPU, these DMA sampling systems sample the analog input signal to generate a sample which is provided to the memory via the bus under control of the DMA sampling systems. Thereafter, such DMA sampling systems advise the CPU that the DMA operation has been completed, and the CPU resumes bus mastership.
Because the time difference between the request for bus mastership from such DMA sampling systems and the grant of bus mastership from the CPU may vary, an exact sampling rate is generally not maintained by such DMA sampling systems since sampling of the analog input signal occurs only after the grant of bus mastership in such DMA sampling systems.
Certain applications of DMA sampling system require that an exact sampling rate be maintained. For example, in fast-Fourier transform (FFT) processing, maintenance of an exact sampling rate is particularly critical to avoid the introduction of noise into the FFT processing algorithm. For example, assuming a dynamic range (i.e., the ratio of the specified maximum signal level capability of a system to its noise level) of 6 decibels per bit, a DMA sampler using an eight-bit sample potentially has a dynamic range of 48 decibels (8 bits.times.6 decibels per bit). However, an error in the sampling rate of as little as 1.5% translates into a 9.5 decibel degradation in dynamic range for the DMA sampling system. Such degradation is referred to as "aperture jitter".